UK inflation: Will September CPI reach 3.5% on 21 October?

By AtheneNet Economy Desk | 26 September 2026

The Office for National Statistics (ONS) reported that UK annual Consumer Prices Index (CPI) inflation rose to 3.1% in August 2026, from 2.9% in July. That puts the rate 0.4 percentage points below the 3.5% threshold in this forecast. Households will get the September figure when the ONS publishes its next inflation bulletin, scheduled for 21 October at 7:00am. The question is whether the annual rate will rise again—and what that reading would mean for everyday prices.

The September CPI question at a glance

• Will the initially published September 2026 annual all-items CPI rate be at least 3.5%?
• Deadline: 21 October 2026, the scheduled date of the September inflation bulletin.
• YES: The first ONS bulletin reports 3.5% or higher for annual all-items CPI.
• NO: The first bulletin reports an annual all-items CPI rate below 3.5%.
• Deciding result: The CPI figure in the ONS September 2026 consumer price inflation bulletin, scheduled for 7:00am.

August’s rise leaves a clear gap to 3.5%

In its August 2026 inflation bulletin, the ONS put annual CPI inflation at 3.1%, up from 2.9% in July. The increase was 0.2 percentage points. Reaching 3.5% in September would require a further rise of at least 0.4 percentage points from August’s published rate.

The ONS said transport, particularly motor fuels, made the largest upward contribution to the change in the annual CPI and CPIH rates in August. That identifies a significant driver of the latest rise. It does not establish where fuel prices—or the overall inflation rate—will go in September.

The August figure is the latest published result available for this comparison, not a September estimate. It gives the forecast a starting point, while the 3.5% line makes the outcome measurable. A reading of 3.4% would settle the question differently from a reading of 3.5%, even though the difference between those rates is small for any one household’s spending.

What the CPI rate says about living costs

CPI tracks changes over time in the prices of a basket of goods and services bought by households. The annual all-items rate compares that basket’s measured price level with its level in the same month a year earlier. September’s headline rate will therefore describe an annual change across the basket, not the change in one person’s bill since August.

An annual rate of 3.5% would mean the measured CPI basket was 3.5% more expensive than a year earlier. It would not mean every product rose by 3.5%, or that a household’s total monthly outgoings increased by exactly that amount. People buy different things in different proportions, so their experience can diverge from the headline measure.

There is also a distinction between inflation slowing and prices falling. If annual CPI eased from 3.1% to 2.8%, the basket would still be more expensive than a year earlier; its annual pace of increase would simply be slower. A fall in the overall measured price level is a different outcome. The headline annual rate alone also cannot tell a shopper whether the price of a particular item fell between August and September.

That distinction matters when comparing a new inflation headline with receipts, rent payments or travel costs. A lower annual rate may bring some relief to the pace at which costs rise, but it does not undo earlier increases. Likewise, a higher rate does not show that every cost is accelerating.

Why August’s fuel contribution cannot decide September

Motor fuels helped push up the annual rate in August, according to the ONS. September’s result will depend on the prices recorded for that month and how they compare with September 2025 across the CPI basket. Other categories can pull in different directions, so August’s leading contributor cannot be treated as a forecast for the next release.

The annual comparison can also shift when the prices from a year earlier change. For that reason, a headline rate may move even when a reader’s most noticeable recent purchase has not. The decisive number is the published all-items annual rate, rather than a single fuel price, shop receipt or monthly movement.

There are credible paths on either side of the threshold. If the combined annual price changes across the basket lift CPI to 3.5% or above, the answer is YES. If they leave it at 3.4% or below, the answer is NO. The available August bulletin establishes the starting rate and its main upward contribution; it does not establish which path September will take.

CPI, CPIH and the number that settles this forecast

UK inflation coverage can refer to several measures. This forecast uses CPI, the Consumer Prices Index, and specifically its annual all-items rate for September 2026. It does not use CPIH, which is a separate measure that includes owner occupiers’ housing costs. The ONS discusses both measures in its inflation releases, so the label beside the number matters.

The comparison is also annual, rather than month on month. A monthly percentage change describes movement since the previous month; the annual rate compares with the same month one year before. Either may be useful for understanding price movements, but only the annual all-items CPI rate answers this question.

For resolution, use the figure in the first ONS September 2026 bulletin. A later revision or a figure quoted from a subsequent publication does not change this forecast’s result. At exactly 3.5%, the answer is YES; any initially published figure below 3.5% is NO. The rule depends on the reported figure, without substituting an estimate or another inflation index.

What households can take from the October release

The 21 October bulletin will provide a national measure of price change, not a prediction of an individual household’s next bill. Readers assessing their own costs can compare the headline with categories that matter to them, while remembering that the overall rate combines many purchases. The explanation of category contributions may help show why the headline moved.

It is useful to keep three questions separate when the result arrives: Did the annual CPI rate cross 3.5%? Did it rise or fall relative to August’s 3.1%? And which prices contributed most to that change? Each answers something different. A result below 3.5% could still be higher than August’s rate, while a result above the threshold would show faster annual inflation than in August.

The next check is the ONS September 2026 consumer price inflation bulletin, scheduled for 7:00am on 21 October. Its initially published annual all-items CPI figure will settle the forecast and provide the detail needed to interpret what changed for UK living costs.

Source: Office for National Statistics